Several people have reported an issue in which making or receiving a FaceTime call fails on their iPad, iPhone and iPod Touch.
FaceTime is not available in every country.
Make sure FaceTime is enabled: Settings > FaceTime.
Ensure that camera and FaceTime are not disabled in Settings > General > Restrictions.
Make sure that both parties have an active Internet connection.
Try re-enabling FaceTime by tapping Settings > FaceTime and toggle off and on again.
If problem persists:
Restart your iOS (iPad, iPhone and iPod Touch) device by pressing and holding the Sleep/Wake button for a few seconds, and then slide the slider.
If restarting doesn’t fix it:
It has been reported that changing your DNS settings fixes this issue: Settings > Wi-Fi > then select the blue arrow next to your current Wi-Fi network and then tap the “DNS” field and enter the DNS servers; 188.8.131.52 (Google’s Public DNS).